| 摘要 |
PURPOSE:To eliminate an outside attached component and to lower the cost of the title apparatus by a method wherein a pulse-width modulation output is formed as a three-value output. CONSTITUTION:A control IC 11 outputs a high level (H) in order to obtain a gain at its start. When the rotation state of a motor is brought close to a steady state (e.g. when it is set to + or -5% of a target constant-speed control operation), it is changed over to a 2.5-V pulse-width modulation output at a sidle level (M), and the motor is driven directly at a duty ratio of 50%. That is to say, until the cycle of a rotational-speed detection signal FG reaches + or -5% of a target, a transistor(Tr) control circuit 22 turns on a Tr 21 and turns off a Tr 22, and an H voltage as a constant voltage is output from a pulse-width modulation output terminal. When it reaches within + or -5% of a target frequency, the Tr control circuit 22 turns off the Tr 21 and turns on/off the Tr 22. Consequently, the output of a pulse-width modulation is set to an M-voltage to an L-voltage (0V). |
